Electric control device



Feb. 18,.l947. L. J. DAHLINE ETAL 2,416,159

ELECTRIC CONTROL DEVICE Filed March 13, 1944 5 $heets-$heet 2 Inventors ahline and flttcr 197 7//%% INSULATION .Lawrence J. D I

M/flliam J. Field 7 I @L/M Feb. 18, 194.7.

L. J. DAHLINE ETAL 2,

ELEC'IRIQ CONTROL DEVICE 7 Filed March 13, 1944 I 3 Sheets-Sheet 3 14$ 77 15 1 1&1 2 514 I mhmu 7 a 11? I I'm/among Lawrence J. Dahl'uqe and \h/illiam 6. field Patented Feb. 1a, 1947 2,416,159 7 ELECTRIC CONTROL DEVICE Lawrence J. Dahline and William J. Field, Minneapolis, Minn., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a

corporation of Delaware Application March 13, 1944, Serial No. 526,288

15 Claims. (Cl. 171-242) Our invention relates to electric control devices and has for an object to produce a control device responsive to a feeble variable actuating force and operating to produce an appreciable corresponding controlling force.

Another object of the invention resides in providing a control device which requires an exceedingly small amount of energy to operate.

A feature of the invention resides in providing a control device which will produce force or movement of the controlled member substantially proportional to the torque or movement of the actuating member.

A feature of the invention resides in providing an electric control device which will be unaffected by the operation of another control device or other electric apparatus positioned in the vicinity thereof.

A still further object of the invention resides in providing an electric control device in which flexible leads, slip rings or other sliding contacts are eliminated.

Another object of the invention resides in providing a control device which will be simple in construction and positive and efiective in operation.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/or described.

In the drawings:

Fig. 1 is a plan view of an electric control device illustrating an embodiment of our invention.

Fig. 2 is an elevational view, parts being sectioned along the line 22 of Fig. 1.

Fig. 3 is an elevational view, parts being sectioned along the line 33 of Fig. 1.

Fig. 4 is a plan view, parts being sectioned along the line 4-4 of Fig. 2.

Fig. 5 is a perspective view of the rotor used with the device illustrated in Figs. 1 and 4.

Figs. 6, 7, 8 and 9 are perspective views of different forms of rotors capable of use with our invention.

Fig. 10 is a Wiring diagram of a circuit in which our invention may be used.

In control devices of the prior art, considerable force or torque is required to move the operating member of the device. The present invention overcomes this objection by providing a, construction utilizing the principle of eddy currents and in which an extremely small resistance to the movement of the operating member of the device results so that the device is responsive to relatively weak actuating forces.

Our invention comprises a magnetic core structure 2!, operating in conjunction with which is a rotor 22 functioning as a short-circuited conductor indicated in its entirety by the reference numeral 23, and comprising a member having the shape of a deformed or incomplete cylinder. The core structure 2i is supported on a base 24, while the rotor 22 is supported for rotation by means of a frame 25 also carri d by said base. These parts will now be described in detail.

The core structure 2| is constructed from a number of laminations 26 which are E-shaped in form an which, when assembled, form the core structure 25 also E-shaped in form, which has a center leg 21 and two outer legs and 29 nected together by means of a yoke or connecting portion IN. The upper end of the leg 2'! has attached to it a transverse core member ,32 which is held in place between the outermost laminations 26a of the core structure 2! by means of rivets 33 which extend jointly through said laminations and transverse core member. The core member 32 has opposing ends 34 and 35 which lie in proximity to the facing surfaces 36 and 3'! of the legs 28 and 29, and form air gaps 38 and 39 therebetween. The core structure 2i is attached to the base 24 which is preferably formed of insulating material by means of two clip angles 4| whichare secured to the connecting portion 3i ofthe core structure by means of a rivet 42.

Screws 43 pass through these clip angles and are threaded into the base 24.

Mounted on the center leg 2! of the core structure 2| is an exciting winding 44 which is energized by a suitable pulsating current such as an alternating current or the like and which causes flux to pass through two parallel magnetic circuits indicated diagrammatically at 41 and 48, the circuit 41 including the air gap 38 and the leg 28'of the core structure and the circuit 48 including the air gap 39 and the leg 29 of the core structure. The core structure 2| is so constructed that the fluxes set up in these two circuits by the winding 44 are balanced. On the legs 28 and 29 are mounted control windings 45 and 46 which are responsive to the fluxes passing in the two magnetic circuits 4? and 48.

The rotor 22 is best shown in Fig. 5 and consists of a shaft 5! which has attached o it a head 52. Extending downwardly from the head52 is an annular part 53 which constitutes a conductor indicated in its entirety by the reference numeral 23. In the forms of the invention disclosed,

the conductor 23, the head 52 and the shaft are all constructed integral, though it can be readily comprehended that these parts may be separately formed and also that the head 52 may, if desired, be constructed of insulating material. Where, however, the head 52 is constructed of conducting material, the same as the annular part 53, the said head forms part of the conductor and operates in conjunction therewith, as will be subsequently more fully described.

The frame 25 includes a cross bar 55 which is formed with a bearing 54 in which the shaft 5| of rotor 22 is journaled. Thefram'e 25 further includes two posts 56 and 51 which are secured to the base 24 by means of screws 58. Other screws 59 extend through the cross-bar 55 and are threaded into the posts 56 and 51 and secure said cross-bar in position to support the rotor 22 for rotation. A washer 66 disposed between the cross-bar 55 and the head 52 of the rotor, holds thesaid head in spaced relation relative to said cross bar. A collar 6|, secured to the outermost end of the shaft 5| by means of a set screw 62, serves to prevent the shaft 5| from moving, downwardly along the hearing 54. The protruding end 63 of shaft 5| is connected to the movable element of the actuating device which provides the actuating force or torque and serves to operate the control device. This may be accomplished in any suitable manner by means of gearing, mechanical transmission or'by directly attaching the rotor 52 to a movable member movable with the movable element of the actuating device. Where the rotor 22 is directly connected, the shaft 5i and the bearing 54 may be dispensed with and the device will operate with less resistance.

The conductor 23 has a slit 64 formed therein which extends transversely of the circumferential extent of the said conductor. This slit has a part 65 which extends through the annular part 53 of the conductor, Fig. 3, and also a part 66 which extends into the head 52. By means of this slit, the conductor 23 is divided into two of the same adapted to receive the leg 21 of the core structure 2|. This conductor has a slit I93 at the forward portion of the same which can be adjusted angularly about the center of the legr 2l by rotating said conductor about the center' of the leg 21 as an axis. The conductor I9I overlies a disk I94 of insulating material which ha's'a rectangular hole I95 in the same which snugly fits the leg 21 of core structure 2| and prevents rotation of said disk. The disk I94 is provided with an ear I96 projecting rearwardly therefrom. A bolt I91 extends jointlythrough said ear and through a'slot I98 formed in a rearwardly projecting portion I99 of the contherein produces counterfiuxes which unequally portions 67 and 68 which extend up to said slit Y perpendicular to the line joining the centers of the poles of the core structure. Portions 6i and 66 of the rotor then offer equal impedance to the flow of eddy currents in response to the equal magnetic fluxes in magnetic circuits 4i and 48: the eddy currents are equal and these currents in turn produce equal counter fluxes. The counter fluxes are in directions to" oppose the original fluxes, andaccordingly the resultant fluxes are equal; they traverse the windings 45 and 46, and if the windings are identical equal voltages are introduced therein.

If rotor 22 is not in itsv normal position, the impedances of portions 61 and 68 thereof to eddy currents are no longer equal, and the eddy currents caused by the equal magnetic flux are also no longer equal. The counter fluxes are. also unequal in the same sense, and these counter fluxes oppose the normally equal fluxes to give unequal resultant fluxes in the windings 45 and 46, thus changing the relation between the voltages inopposes the fluxes passing through the circuits 41 and 48, depending upon the direction of the slot I93 with reference to the plane of the magnetic circuits 41 and 48. By properly adjusting the conductor I9 I, these counter fluxes can be made to cause the potential across the coils 45 and 46 to become exactly equal, when the rotor is in normal position.

In Fig. 10, we have shown a wiring diagram of an electric circuit utilizing our invention. In this circuit, two electron discharge tubes III and H2 are employed, each having the usual plate or anode H3, grid II4 and cathode II5. In addition, a, heater I I6 is employed for each cath-" ode which causes operation of the. tube in the usual manner. Inasmuch as the circuit for energizing the heaters H6 is well known in the art and forms no particular feature of the invention, the same has not been shown in the drawings.

For energizing the tubes III and H2, a transformer II! is employed having a secondary II8 provided with a center tap I I9 and a primary |2I connected to aline I22--I23 energized from any suitable source of alternating current. In the drawings, one side I23 of the line has been shown as grounded and corresponding parts of the circuit have been shown as grounded as will be presently brought out. One end of the secondary IIB of transformer II! is connected by means of a. conductor I24 with the plate 3 of tube I I2 while the other end of said secondary is connected by means of a conductor I25 with the plate II3 of tube III. The center tap III) of the secondary I I9 is connected by means of a conductor I26 with a condenser I21 which, in turn, is connected by means of conductors I28 and I29 with both of the two cathodes N5 of the tubes III and H2. 'At the same time, the conductor I28 is grounded.

The two grids I I4 of tubes I I I and 2 are connected in parallel by means of conductors I3I and I32 to an amplifier I33. The amplifier I33 may be an ordinary single or multiple stage ampli-.

detail, though it can readily be comprehended that any of the well known types or amplifiers may be used. I

To procure grid bias for the two grids ii a battery lI is employed which is connected by means or a conductor I52 to a resistance The said resistance is in turn connected by means of a. conductor 154 to the conductor $35.

A condenser I55 is grounded through a conductor I56 and is further connected by means. of a conductor I51 to the conductor i3i.

In the embodiment of the invention disclosed in Fig. of the drawings, three control devices 0a, use and Mlle have been illustrated which are connected in series in a circuit which we have termed a control circuit and which is designated by the reference niunerai 55d. For the sake oi simplicity, the same reference numerals as previously employed, modified by a sliderentiating sub-character, will be used to refer to the various similar parts of said control devices. The windings 45a and 46s are connected together by means of a conductor id id and in such a mannor that the potentials set up in these windings tend to oppose each other and in the normal position of the rotor 22a just heutralize each other and produce no flow of current. The windings 45b and 46b and the windings 55c and 5c are similarly connected by means of conductors idlb and Mic. All of these windings are connected in series through conductors M2, M3, Md and I45, the conductor M5 being grounded. Conductor I42 is connected to a blocking condenser I46 which, in turn, is connected by means of a conductor 151 to the'amplifier l33.

The windings Ma, Mb and 4&0 are all con-' nected in parallel through conductors 353, 559 and I SI. These conductors, in turn, are connected to a conductor I82 which is connected to v the side I22 of the line; The said windings Ma, 4417 and 440 are further connected by means of conductors I83, 454 and I85 to ground. It will thus be readily comprehended that the windings 44a, 44b and 440 are throughout the operation of the device constantly energized by the line voltage. I

The controlling element of our improved control device comprises a two-phase electric motor diagrammatically indicated at I351. This motor consists of a rotor IE6 having short-circuited windings; as for example, a squirrel cage. and two stationary windings it'll, led, disposed 90 electrical degrees apart, The rotor 26B is reversible and the direction of rotation is dependent upon the phase relationship of the voltage of the said windings. Both of the windings I51 and i613 are connected to a common conductor I69 which is grounded. The winding 16'! is further connected by means of a conductor Ill to the conductor I28 at a locality between the condenser I'ZI and the tap H9. The winding I 68 is connected by means of a conductor I12 with a condenser H3, which, in turn, is connected by means of a conductor I74 with the side I22 of'the line. It will thus be seen that the winding M8 is directly energized from the line, while the winding It? is energized from the voltage across the plate circuits of the two tubes ill and H2.

In Fig. 10, we have shown as previously stated, three control devices connected in the circuit. Such an installation is particularly useful where three variable actuating devices all function to modify the performance of a single device.

The operation of the invention is as follows: With the actuating devices exerting no torque on the rotors 22a, 22b and 220, said rotors would all be in normal position, and no current would-flow through any oi the windings 55c, ita, d522, d622,

and ddc. Therefore, no voltage would be impressed upon the amplifier I33 and likewise, no signal voltage would be impressed upon the grids lid of the two tubes 9 It and I it. The winding it! or" would thus be deenergized and the motor would remain stationary. Ii, however, one or the rotors 22a, 221) or 220 were shifted out of normal position, a current would be caused to flow through the amplifier I33 and the phase of the current would depend upon the direction of shift of the said rotor. Movement of the said rotor from one side of the normal position to the other would procure reversal in phase and the degree of shift would determine the voltage inipressed upon the amplifier iSB; Since the tubes III and I I2 only transmit current in one direction, one o! the said tubes would serve "to furnish a unidirectional pulsating current through the plate circuit of the tubes. The condenser I2? serves to convert this current into an alternating current which is impressed upon the'winding !61. The value of the condenser i2: can be made such that the voltage impressed upon the winding IE0 is either or 270 out of phase with the voltage across the winding its, depending upon which of the tubes Ill or H2 is passing current. Thus, the motor ltd will be energized as a two-phase motor and the direction of rotation of the same will depend upon the direction of shift of any of the rotors 22a, 22?) or 220. The motor I613 being connected to the device to be controlled, corrects the position of the device until the particular rotor 22a, 221) or 220 which actuated the control device returns to normal position.

In Figs. 6, 7, 8 and 9, we have shown various modifications of the rotor 22 shown in Fig. 5 which modifications produce variations in performance of the control device. These various rotors are similar in construction and for the sake of simplicity, the description of each device will not be repeated and similar reference charac- .ters, to which have been added difierent subcharacters, will be used to designate corresponding parts.

The rotor 22 may, if desired, be constructed as shown in Fig. 8, with the slot dd substantially closed, as indicated at I3I.- With the rotor so constructed, maximum shielding is procured, so that the device is less affected by stray magnetic fields. With thlsform of the invention, however, the sensitivity at normal position is not as great as with that shown in Fig. 5.

In Fig. 7, the slot has been expanded until the shape of the rotor ishemicylindrical. With this form of the invention, the voltage at normal position never quite reaches zero, so that an initial voltage tending to operate the device is always present, which makes the device more sensitive at such position. However, in this case, the shielding eifect isconsiderably lesspronounced.

Where it becomes desirable to produce a device in which the voltage impressed on the amplifier varies proportionately with the angle of displacement of the rotor, a rotor shaped as indicated at Fig. 8 can be employed. It will here be noted that the lower edge I82 of the rotor is in the form of a helix, so that the length of the annular part 53y of the said rotor progressively increases in a direction away from the slot 54 It has been found that a device so constructed produces the I desired results almost up totfipointwhere the The device canbe constructed so as to produce different types of performance in accordance with the requirements. If desired, diflerent degrees of shielding can be procured so as to prevent interference from other control devices or other electrical apparatus. The device is simple in construction and positive in action. With our invention, there are no flexible leads, slip rings, brushes or other movable contacts associated with the rotor of the invention. The moving part of our invention requires a minimum amount of energy to operate and, in certain appl ications, may be directly connected to the actuating member, whereby bearing friction of the control device is entirely eliminated.

Changes in the specific form of our invention, as herein described, may be made within the scope of what is-claimed. without departing from the spirit of our invention.

Having described our invention, what we claim as new and desire to protect by Letters Patent is:

I 1. An electric control device comprising a magnetic core structure providing two magnetic circuits each including a single air gap, means which upon energization is adapted to produce opposed pulsating magnetic fluxes in said circuits normally balancing one another, a short circuited conductor having portions adapted to extend into said air gaps, said conductor being formed with a single slit therein disposed exteriorly of the air gaps and between said portions, means for supporting said conductor for movement to cause said slit to approach one air gap and to recede from the other airgap to unbalance the fluxes in said circuits and flux responsive means actuated through unbalance of the fluxes in said magnetic circuits.

' 2. An electric control device comprising a magnetic core structure providing two magnetic circuits each including a single air gap, means which upon energization is adapted to produce opposed pulsating magnetic fluxes in said circuits, normally balancing one another, a single annular short circuited nonmagnetic conductor having portions adapted to extend into said air gaps, said conductor being formed with a transverse slit extending in the direction of the axis thereof and separating said portions; meansfor supporting said conductor for rotation about its axis to cause said slit to approach one air gap and recede from the other air gap upon rotation bf said conductor in one direction to unbalance the fluxes in said circuits and flux responsive means actuated through unbalance of the fluxes in said circuits.

3. An electric control device comprising a magnetic core structure providing two magnetic circuits each including an air gap, means which upon energization is adapted to produce opposed pulsating magnetic fluxes in said circuits, normally balancing one another, an annular short portions, said conductor being constructed so that the cross-sectional area thereof increases progressively to each side of the slit, means for supporting said conductor for rotation about its axis to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits, and flux responsive means actuated through unbalance of the fluxes in said air gaps.

4. An electric control device comprising a magnetic core structure providing two magnetic circuits each including an air gap, means which upon energization is. adapted to produce opposed pulsating magnetic fluxes in said circuits, normally balancing one another, an annular short circuited conductor having portions adapted to extend into saidair gaps, said conductor being formed with a transverse slit separating said portions, said conductor being constructed so that 'the cross-sectional area thereof varies progressively to each side of the slit, means for supportingsaid conductor for rotation about its axis to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits, and flux responsive means actuated through unbalance of the fluxes in said air gaps.

5. An electric control device comprising a magnetic core structure providing two magnetic circuits each including an air gap, means which upon energization is adapted to produce opposed pulsating magnetic fluxes in said circuits, normally balancing one another, a single tubular short circuited conductor having portions adapted to extend into said air gaps, said conductor being formed with a single transverse slit separating said portions, the axial extent of said tubular conductor varyin progressively to each side of the slit, means for supporting said conductor for rotation about its axis to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits, and flux responsive means actuated through unbalance of the fluxes in said circuits.

6. An electric control device comprising a magnetic core structure E-shaped in form and having a center leg and outer legs forming two spaced air gaps therebetween, said legs providing two magnetic circuits each including one of said air gaps, means which upon energization is adapted to produce opposed pulsating magnetic fluxes in said circuits normally balancing one another, an annular short circuited conductor encircling said center leg and having portions adapted to extend into said air gaps, said conductor being formed with a single transverse slit parallel with the axis thereof and separating said portions, means for supporting said conductor for rotation about its axis, said axis extending longitudinally of the center leg to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits, and flux responsive means actuated through unbalance of the fluxes in said circuits.

7. An electric control device comprising a magnetic core structure E shaped in form and having a center 18g and outer legs forming two spaced air gaps therebetween, said legs providing two magnetic circuits each including one of said air gaps, a winding on said center leg adapted upon energization to produce opposed pulsating magnetic fluxes in' said circuits, normally balancing one another, an annular short circulted conductor encirclin said center leg and enveloping and shielding said winding, said conductor having portions adapted to extend into said air gaps, and being formed with a single transverse slit parallel with the axis thereof and separating said portions, means for supporting said conductor for rotation about an axis extending longitudinally of the center leg to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits and flux responsive means actuated through unbalance of the fluxes in said circuits including windings on said outer legs.

8. An electric control device comprising a magnetic core structure E-shaped in form'and having a center leg and outer legs forming two spaced air gaps therebetween, said legs providing two magnetic circuits each including one of said air gaps, a winding on said center leg adapted upon energization to produce opposed pulsating magnetic fluxes in said circuits normally balancing one another, a cup shaped short circuited conductor having a head and an annular part encircling said center leg and said Winding with its axis extending in the direction of extent of said center leg and with portions extending into said air gaps, said conductor being formed with a slit extending transversely of the circumferential extent thereof and separating said portions, means for supportin said conductor for rotation about its axis, to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said circuits, and flux responsive means actuated through unbalance of the fluxes in said circuits.

9. An electric control device comprising a magnetic core structure E-shaped in form and having a center leg and outer legs forming two spaced air gaps therebetween, said legs providing two magnetic circuits each including one of said air gaps, a winding on said center leg adapted upon energization to produce opposed pulsating magnetic fluxes in said circuits normally balancing one another, a cup shaped short circuited conductor having a head and an annular part encircling said center leg and said winding and having portions adapted to extend into said air gaps, said conductor being formed with a slit extending transversely of the circumferential extent thereof and separating said portions, means for supporting said conductor for rotation about an axis extending longitudinally of the center leg, to cause said slit to approach one air gap and recede from the other air gap upon rotation of said conductor in one direction to unbalance the fluxes in said air gaps and a second short circuited conductor encircling said center leg and cooperating with said first named conductor to shield said winding.

10. In combination, a control circuit, a control device comprising a magnetic core structure providing two magnetic circuits each including an air gap, exciting means for producing in said air gaps opposed pulsating magnetic fluxes normally balancing one another, a short circuited conductcr havin portions adapted to extend into said air gaps, means forsupporting said condu'ctor for movement to cause said portions to move transversely of the direction of extent of the air gaps, to unbalance the fluxes in said air gaps, current conducting means responsive to unlo balance of th fluxes-in said air gaps, said cur= rent conducting means being connected in said control circuit and a second control device sini= iiar to said first named control device and excited by the some exciting means, the current conducting means of said second control device being connected in said control circuit and in series with the current conducting means of said first named control device and a second short circuited conductor associated with the short circuited conductor of said first named control device and adjustable relative thereto to vary the phase relas tion between said first named device and said second named device.

11 In combination, a control circuit, a mag netic core structure providing two magnetic cir cults, exciting means for producing opposed pulsatin magnetic fluxes in said circuits nor-= mally balancing one another, a short circulted conductor having portions adapted to intercept the fluxes passing through said circuits, means for supporting said conductor for movement to cause said portions to move transversely of the direction of extent of the fluxes in said circuits to unbalance the fluxes in said circuits, current conducting means responsive to unbalance of the iiuxes in said magnetic circuits, said current conducting means being connected in said con trol circuit and a second control device similar to said first named control device, the current conducting means of said second control device being connected in said control circuit and in series with the current conducting means of said first named control device and a second short circuited conductor associated with the short circuited conductor of said first named control de= vice and adjustable relative thereto to vary the phase relation between said first named device and said second named device.

12. An electric control device comprising magnetic core means providing a plurality of pairs of magnetic circuits, means which upon energization is adapted to produce pulsating magnetlc fluxes in all of said magnetic circuits with the fluxes in each pair of magnetic circuits balancing one another, a plurality of short circuited conductors, one for each pair of magnetic circuits, each of said conductors having a portion adapted to intercept the fluxes passing through each of the magnetic circuits of the pair, means for supporting each of said conductors for independent movement to cause the denoted portions of said conductors to move transversely of the direction of extent of the fluxes intercepted by them to unbalance said fluxes some of said magnetic circuits having a' second short circuited conductor associated with the first named short circuited conductor thereof, said second short circuited magnetic core structure providing two'magnetic circuits, a single air gap in each of said circuits, said magnetic circuits having a common leg provided with two poles and with other legs having 'complemental poles spaced from said first named poles and forming said air gaps, means which on energization is adapted to produce in said magnetic circuits balanced pulsating fluxes, both of i3. An electric control device comprising a- 11 which at certain instants flow in the same direc- -tlon from the poles of said common leg through said air gaps and to the complemental poles of the other legs, a short circuited conductor having circuitous extent with portions extending into said air gaps, said conductor being formed with a single slit therein extending transversely of the direction of extent thereof and separating said portions, said slit being disposed exteriorly of and intermediate said air gaps, means for supporting said conductor for movement in the direction of extent thereof to cause said slit to approach one air gap and to recede from the other air gap to unbalance the fluxes in said circuits and flux responsive means actuated through unbalance of the fluxes in said magnetic circuits.

14. An electric control device comprising a magnetic core structure providing two magnetic circuits, a single air gap in each of said circuits, said magnetic circuits having a common leg provided with two poles and with other legs having complemental poles spaced from said first named poles and forming said air gaps, a winding on said common leg which on energization is adapted to produce in said circuits balanced pulsating fluxes, both of which at certain instants flow in the same direction from the poles of said common leg, through said air gaps to the complemental poles of the other legs, a cup-shaped short circuited conductor encircling the poles of said common leg and having portions extending into said air gaps, said conductor bein formed with a single slit therein extending along an element of said conductor and separating said portions, said slit being disposed exteriorly of and intermediate said air gaps, means for supporting said conductor for movement about the axis of said conductor, said axis being located at the axis of said common leg, said conductor enveloping said winding about the sides and one end thereof, a 40 6 disk-like short-circuited conductor disposed at the open end of said cup-shaped conductor and further enveloping said winding, said second conductor having a slit therein disposed exteriorly 5 of and intermediate said air gaps, means for adjustably supporting said second conductor and flux responsive means actuated through unbalance of the fluxes in said magnetic circuits.

15. An electric control device comprising a magnetic core structure providing two magnetic circuits, a single air gap in each of said circuits, said magnetic circuits having a common leg provided with two poles and with other legs having complemental poles spaced from said first named poles and forming said air gaps, means which on energization is adapted to produce in said magnetic circuits balanced pulsating fluxes, both oi. which at certain instants flow in the same direction from the poles ofsaid common leg '20 through said air gaps and to the complemental poles of the other legs, a C-shaped short circuited conductor encirclin said common leg and having portions extending into said air gaps,

means for supporting said conductor for move 'ment in the direction of extent thereof to un- WILLIAM J. FIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Number 2,207,248 Garlick July 9, 1940 Herz Jan. 1, 1924 

